peters



UNITED sat/@Es PATENT OEEIOE.

THOMAS L. MITCHELL, OF BIRKENHEAD, ENGLAND.

PROPELLING VESSELS.

Speccation of Letters Patent No. 9,831, dated July 5, 1853.

To all whom t may concern Be it` known that l, THOMAS 'LIVINGSTON MITCHELL, of Birkenhead, near Liverpool, in the county of Lancaster, England, a subject of the Queen of Great Britain, have invented or discovered new and useful Tmprovements in Propelling Vessels; and I, the said THOMAS LIVINGSTON MITCHELL, do hereby declare that the nature of the said invention and the manner in which the same is to Vbe performed are fully described and ascertained in and by the following statement thereof, reference being had to the drawings hereunto annexed and to the iigures and letters marked thereon-that is to say:

The invention consists of applying an instrument in the nature of a boomerang placed in a suitable axis as a propeller for propelling vessels, and in order that the invention may be most fully understood and readily carried into effect I will proceed to describe the invention.

Description of the drawing-On observing the motion of boomerang it is found to describe in its rotary movement in the air a whirl around a hollow center, leaving a vacant center of gravity and it suggested itself to the mind of the said THOMAS Liv- INGSTON MITCHELL that this center might be in a line such a, Z), Figure l, dividing the two eccentric parts, so that they should be together equal in surface to the remaining l central portion, and on experiment this vie'w was confirmed, and he considers that this will prove to be the best form for the application of the screw principle in propelling vessels. F ig. 2 shows the propeller in different positions and it will be perceived that the edges opposed to the water at Z and e work in it obliquely to the radius of rotary motion f g much in the manner in which a shell-auger penetrates wood, and it will be obvious that in this construction there will be no tendency to throw the water into a cone. Fig. 3 shows an edge View of the propeller' and axis. Great velocity of rotatory movement appears to be d-esirable for the purposes of propulsion' when the screw principle is applied. This is to be attained by the present arrangement where there is least lateral resistance. A thin edge working in the water obliquely can offer little obstruction and at the center, where motion is slowest, the given power is kept clear of the plane of the screw. This propeller works in the center plane of a screw except at the center and with edges meeting both the concentric and the lateral resistances obliquely. The pitch of the spiral blade or screw may be varied. The propeller may be made with a concave and a flat surface or with two flat or twoconcave surfaces. Then two flat surfaces however are used it will be desirable to chamfer off the edges. The propellers thus formed..are suitable to be applied in like manner to the screw and such like propellers heretofore used, and more than one suc-h blade may be applied; but it is considered that one blade is the best. Figs. 4L and 5 show two diagrams of such a propeller supposing it to be in action, from I which figures it will be evident that the two ends of the propeller work in the thread of the same screw. The leading end a cutting into the water with a thin edge may be termed the fang, the following end b, taking the water obliquely and operating against the water, so as to make its resistance afford a purchase to drive forward, this may be called the tail or fin. It will be evident that in turning the palm in the opposite direction the action of o and b will be reversed, the fang becoming the lin and vice versa. There is much in this peculiar difference between the real screw and the rotatory paddles now in use that will prove by experience how important it will be for the attainment of high speed to adopt the true principle of the screw. The rotatory paddles or palms if considered as screws may be said to describe the threads of a double screw each presenting a plane which when in motion is opposed obliquely to a fluid which must be thrown thereby into circular or eccentric motion, whereas the thin edge of a., 7), passes easily without opposing any surface to lateral resistance through the water and obtains from the resist-ance of the fluid a propelling power which may be increased in proportion to the velocity.

In the instruments hitherto used called screw propellers the lateral resistance encountered in all attempts at high speed must be insurmountable if according to Hutton the resistance to a plane by a fluid acting in a direction perpendicular to its face is equal to the weight of a column of the fluid .whose base is the plane or if the resistance increases as the cube of the velocity it must be obvious that unless the true principle of the screw is applied great velocity through water by means of rotatory motion need not be attempted.

It should be remarked that although I b-elieve that the arrangement above given is the best for oonbining the axis of motion to the boomerang propeller, I do not confine the invention thereto, as variations may be made without departing from the principle of the invention.

The foregoing description, and the diagrams to which it refers explains the theory of the boomerang propeller. I will now proceed to describe the practical application of this theory to the construction of a propeller.

The first thing is to construct a hub (A) Figs. 6 and 7. This hub may extend from l to l, Fig. 6. Then I adapt a boomerang blade (B) to this hub, in an oblique position, as represented. This blade may extend from 2 to 2. The central portion of the blade is made wider on the inner edge than is due to theory to bring it into contact with a larger portion of the surface of the hub, that it may be more firmly united thereto. The instrument thus constructed would act with great eiiiciency in propelling a vessel, but it would be very diiiicult'to apply it to vessels of the ordinary construction because of the great space which the blade occupies in the direction of its axis. To avoid this difficulty I divide the blade in the middle at the line 3, and move that part of it drawn in red lines,Fig. 6, along the hub but, without turning it until it occupies the position represented in black lines (C). The two halves of the blade now occupy the same angular position, with respect to the axis of the hub, that they did before, but the position of the part (C) is changed .with respect to the ends of the hub and the part (B). This division neither disturbs the equilibrium of the propeller blade upon its axis nor in its action upon the water. This substitution of two semi-boomerang blades for one whole one admits of the use of a hub (A) of one half the length required for a single blade; but even this is in many cases inconveniently long. Therefore to render the instrument still shorter, I propose to out the blade, at the lines 3, 4L, and 5, Fig. 8, into four parts, and translate the three parts m, n, and 0, represented in red lines, along the hub to the positions in which they are represented by blacl lines D, E, C. In this case also the several parts of the blade thus subdivided occupy the same angular position relative to the axis of the hub (A) which they would have done had they remained as part of the unmutilated blade attached to the hub in one piece. The action of a whole blade and one divided into two or four parts, arranged as before described, are the same and act with the same efliciency or thereabout to propel the vessel; but the subdivision of the blade renders a propeller constructed upon this principle as compact, or nearly so, as any other of the same diameter.

Fig. 7 represents an end view of the propeller, a side view of which is represented in Fig. G; and Fig. 9 represents an end view of the propeller, the side elevation of which is shown in Fig. 8. These end views show that the diameter and angular position of the blade on the axis are the same, .whether employed whole or mutilated by division as hereinbefor-e described.

I have deemed it unnecessary to give a detailed description ol the boomerang itself, as it is a well known implement of Indian warfare, the form and manner of using which are well ascertained.

Having thus described my improved propeller, What I claim therein as new, and desire to secure by Letters Patent, is,

Constructing the blade or blades of the same upon the principle or in t-he form of the boomerang as herein described and represented.

ir. L. Miroir-inrit.

I/Vitnesses:

THOMAS RIGGE, B. l?. BELL ALLEN. 

